Implantable devices require power source for functional operation. For example, pacemakers have been widely used to stimulate heart muscles and lithium batteries are used to provide power. Emerging technologies such as MEMS (MicroElectroMechanical Systems) promise to improve the quality of life for patients suffer from chronicle diseases. Implantable sensors made by MEMS technology have the advantages of low-cost, small-in-size, easy integration with the controlling integrated circuits (ICs) and low power consumption. However, the size of conventional lithium batteries is large compared to the MEMS-based sensors and post-processing will often be needed to integrate the battery with the sensors.
Published United States Patent Application 20040241528 (Chiao et al 2004) describes a MEMS-based microbial fuel cell in which a silicon substrate is used to fabricate miniature parallel fluid channels having a current collecting coating. Yeast is used as a catalyst. The fuel is glucose and is found in abundance within the human body. When yeast metabolizes glucose, electrons and protons are generated. Electrons are stored in biomolecules, such as NAD, the electrons are transferred to the anode by oxidation/reduction reactions. On the other hand, protons are diffused through a proton exchange membrane (PEM) and collected by the cathode. Electric power can be harvested by connecting the anode and cathode through a dissipating device. The application of the MEMS fuel cell is to provide a powering device that is long-lasting, self-sustain, small-in-size and easy integration with ICs and MEMS sensors.